Measurement and Effects of Heat Science Notes

Measurement and Effects of Heat Science Notes

Important Points:

→ Heat: It is a form of energy. It flows from a body at higher temperature to a body at lower temperature. The total kinetic energy of the atoms in a substance is a measure of the heat contained in that substance.

→ The SI unit of heat is the joule. Heat, being a form of energy, can be expressed in erg also. Heat is also expressed in calorie and kilocalorie.

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Temperature

→ It is a quantitative measure of the degree of hotness or coldness of a body. It decides the direction of flow of heat. The temperature of a substance is related to the average kinetic energy of the atoms in that substance.

→ The SI unit of temperature is the kelvin (K). Temperature is also expressed in °C (degree Celsius) and °F (degree Fahrenheit).

\(\frac{F-32}{9}\) = \(\frac{C}{5}\), K = C + 273.15
∴ F = \(\frac{9}{5}\) C + 32 = (K – 273.15) + 32

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→ Here, C denotes temperature in °C, F denotes temperature in ‘F and K denotes temperature in K (kelvin).

Description °F °C K
Boiling point of water 212 100 373.15
Freezing point of water 32 0 273
Room temperature 72 23 296
Boiling point of mercury 356.7
Freezing point of mercury – 38.8

→  There are different types of thermometers such as that used in a laboratory, clinical thermometer, digital thermometer and maximum-minimum thermometer.

→  Specific heat: The specific heat of an object (a substance) is the amount of heat required to increase the temperature of unit mass of that substance through one degree. It is represented by the symbol c and expressed in different units such as J/(kg. K), J/(kg. °C) and cal/ (g.°C).

Solid Coefficient of linear expansion x 106 (1/°C) Liquid Coefficient of volume expansion x 10 (1/°C) Gas Expansion coefficient x 103 (1/°C)
Copper 17 Alcohol 1.0 Hydrogen 3.66
Aluminium 23.1 Water 0.2 Helium 3.66
Iron 11.5 Mercury 0.2 Nitrogen 3.67
Silver 18 Chloroform 1.3 Sulphur dioxide 3.90

Heat absorbed or given out by a body,
Q = mc(Tf – Ti)
The specific heat of a body can be determined using a calorimeter.

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→ The coefficient of linear expansion of a solid substance,
λ = (l2 – l1)/(l1 ∆ T).

→ The coefficient of areal expansion of a solid substance,
σ = (A2 – A1) / (A1 ∆ T).

→ The volumetric expansion coefficient of a solid substance,
β = (V2 – V1)/(V1 ∆ T).
This formula is also applicable to a liquid

→ The constant pressure expansion coefficient of a gas (the volumetric expansion coefficient at constant pressure)
β = (V2 – V1)/(V1 ∆ T).

→ When a substance is heated, its volume increases, and if the mass is kept constant by enclosing the substance, the density of the substance decreses as density = mass/volume.

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